1. Field of Invention
This invention relates to flat or spade type drill bits, specifically to a drill bit having an improved more versatile cutting surface with a unique center point, for drilling into a non-metallic material such as wood, or other relatively soft material, and used in a hand held powered drill, a manual powered brace or drill press.
2. Discussion of Prior Art
Heretofore, flat or spade type bits emphasized several kinds of points including triangular shaped, diamond shaped and rectangular-triangular shaped center points of rather large size and associated radially extending cutting surfaces. The point has been given various configurations from a flat to a fluted side surface and straight to beveled edges. The radially extending cutting edges are beveled and align at varying angles to the cutting surface. The relatively large center point is employed as a guide and reportedly to improve cutting action and to reduce the magnitude of required torque and thrust. The prior art when used in a hand held powered drill results in a lack of concentric holes when boring into relatively thin materials, since the guidance control diminishes as the large point exits the hole. Splintering at the exit portion of the hole can also be a problem. The typical spade bit is not useful in drilling overlapping holes , nor in drilling holes that enter the workpiece at such an angle that the center point cannot be engaged first. The typical spade bit is not suitable for drilling essentially flat bottomed holes. These things are some of the problems experienced with the prior art that have been addressed in a unique way by the present invention.
The present invention includes a spur or tooth of rectangular cross section located on the ends and at the center of the radially extending cutting surfaces. The spur on the ends performs as an additional guide and improves the concentricity of the hole and reduces splintering at the exit portion of the hole, particularly in thinner work pieces. The outer spurs improve cutting action since the spurs serve to cut separate small chips and provide improved conditions for action of the radially extended cutting surfaces. When used in a drill press or a device for holding a portable power unit in rigid alignment, the spurs on the bit provide guidance to enable the boring of overlapping holes and the spurs also provide guidance in boring holes that enter the work piece at an angle that precludes engaging the center point first. The spurs also make it possible to drill an essentially flat bottomed hole since with the outer spurs present the center spur can be shortened. The rectangular cross section of the outer spurs as opposed to a blade or scoring type configuration spur, improves cutting efficiency and reduces heat buildup during high speed drilling.